This invention relates to a thermal transfer recording medium, to an image-forming method using the thermal transfer recording medium, and to an image-bearing body to be formed from the thermal transfer recording medium. In particular, this invention relates to a thermal transfer recording medium for forming, on an image-receiving sheet, an areal gradation color image by superimposing at least two colors by thermal transfer, in accordance with image data, using a thermal head printer; to an image-forming method using the thermal transfer recording medium; and to an image-bearing body formed from the thermal transfer recording medium.
With respect to the thermal transfer recording system for forming a gradation image by using a thermal head printer, two transfer systems are known to date, i.e. a sublimation transferring system and a melt transferring system.
According to the sublimation transferring system, a thermal transfer recording medium having, on a substrate, a thermal transfer recording layer comprising a sublimating (thermally transferring) dye and a resinous binder is superimposed on an image-receiving sheet. The sublimating dye in the thermal transfer recording layer is allowed to transfer, in accordance with the quantity of heat from a thermal head, to the image-receiving sheet, thereby forming a gradation image.
However, when an image is formed by using a sublimating dye, the image formed is generally poor in durability, so that the application of the sublimation transferring system to the fields where excellency in heat resistance or light-resistance of printed image is demanded would be limited. Further, the thermal transfer recording medium employed in the sublimation transferring system is defective in that since the thermal recording sensitivity of the thermal transfer recording medium is poor as compared with the recording medium employed in the melt transferring system, the thermal transfer recording medium is not suited for use as a high-speed recording material employed in a recording system using a high-resolution thermal head which is expected to be actually employed in future for the miniaturization and lightening of a printer operated with high printing energy and driven by a battery such as a dry battery.
On the other hand, according to the melt transferring system, a transfer sheet bearing, on a substrate, a thermally meltable ink transfer layer comprising a colorant such as dye or pigment and a binder such as wax is superimposed on an image-receiving sheet. Energy is applied to a heating device such as a thermal head in accordance with an image data so as to melt-bond the ink transfer layer to the image-receiving sheet, thereby forming an image. The image formed by the melt-transferring system is excellent in concentration and sharpness and is suited for use in recording a binary image such as letters and linear image.
Further, the melt transferring system can be employed for forming a color image by using a thermal transfer sheet bearing yellow, Magenta, cyan and black ink regions, the thermal transfer sheet being subsequently superimposed on an image-forming sheet so as to obtain a color image. Such a thermal transfer sheet for forming a color image is disclosed in Japanese Patent Publication 63-65029.
However, in the case of the thermal transfer sheet disclosed in this Japanese Patent Publication 63-65029, since a crystalline wax having a low melting point is employed as a binder for the ink layer, the blurring of ink tends to occur, thereby deteriorating the resolution of image. Additionally, the fixing strength of the image transferred is relatively weak, so that when an image portion is strongly rubbed with a finger, the image portion may be removed away.
With a view to solve this problem, various methods have been proposed. For example, a heat sensitive transfer sheet bearing a heat sensitive ink layer comprising not less than 65% of amorphous polymer, a releasable material and a colorant is proposed in Japanese Patent Application Disclosure (Kokai) 61-244592. However, even in the case of the heat sensitive transfer sheet disclosed in this Japanese Patent Disclosure, since a crystalline wax is included in the ink layer, the fixing strength of the portion where a plurality of color images is superimposed is still insufficient.
This invention has been made in view of the aforementioned problems accompanying the prior art, and therefore, an object of this invention is to provide a thermal transfer recording medium which is capable of preventing the resolution of image from deteriorating due to a blur of ink due to the use of crystalline wax of low melting point, and also capable of inhibiting the deterioration of durability of an image that may be caused by the employment of such a wax.
Another object of this invention is to provide a thermal transfer recording medium which is excellent in sharp cutting property of the transfer recording layer upon thermal transferring, is high in optical density of transferred image, and is excellent in halftone expression based on areal gradation of dots.
Another object of this invention is to provide an image-forming method using such a thermal transfer recording medium.
A further object of this invention is to provide an image-bearing body formed by using such a thermal transfer recording medium.
In an attempt to achieve the above object, the present inventors have made intensive studies to find that a thermal transfer recording layer containing a coloring pigment as a colorant, an amorphous organic polymer as a binder, instead of wax, and colorless or light-colored fine particles, at a specific ratio, can exhibit desired properties. The present invention is based on this finding.
Accordingly, this invention provides a thermal transfer recording medium comprising, on a support, a thermal transfer recording layer which contains, as a main constituent, a coloring pigment, an amorphous organic polymer and colorless or light-colored fine particles, and which has a thickness of 0.2 xcexcm to 1.0 xcexcm, the recording layer contains the coloring pigment, the amorphous organic high polymer and the fine particles at a weight ratio of 20-60 parts by weight: 40-70 parts by weight: and 1-30 parts by weight.
According to this invention, there is also provided a method of forming an image by means of a thermal head printer and by using the thermal transfer recording medium of this invention, the method comprising thermally transferring the thermal transfer recording layer to an image-receiving sheet having an image-receiving surface by means of a thermal head printer in accordance with image data to thereby form an areal gradation image, wherein the image-receiving surface of the image-receiving sheet is constituted by the same type of amorphous organic polymer as the amorphous organic polymer included in the thermal transfer recording layer.
According to this invention, there is also provided an image-bearing body comprising an image carrier, and an image region formed on the image carrier, wherein the image region is formed from a thermal transfer recording layer of the thermal transfer recording medium of this invention.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.